I always start off stating my terms are 14 days to commercial clients and 90% of the time they are ok with that, the ones that are not are on 30 day terms and no longer. I have never had a problem generally operating this way and on the odd occassion it does slip I am always on the phone promptly within a day or two of the due date, with a polite but assertive reminder. He who is a constant but polite pain in the ass will always get paid first above those that are to afraid to `hastle` there customers. After a few gentle reminders they will soon get in the habit of paying you on time as they can do without the hastle of knowing that you will reliably be on there case if they don`t, works for me.